1. Field of the Invention
This invention relates to a welding apparatus.
2. Description of the Related Art
Conventionally, as shown in FIG. 10, a welding apparatus provided with an electrode die portion c having a lower base portion a and an upper base portion b elevatable as to close to and part from the lower base portion a, plural lower electrode portions d attached to the lower base portion a, and plural upper electrode portions e attached to the upper base portion b, wherein the upper electrode portion e has a vertical welding electrode pressurizing cylinder gun g which is supplied with cooling water in unpressurized state and pressed to a welded object f placed on the lower electrode portions d to weld in pressurized state, is known. The above welding electrode pressurizing cylinder gun g has a main body portion m, a piston rod portion n inserted to the main body portion m as to freely slide, and a tip electrode portion o arranged on a lower end of the piston rod portion n protruding downward from the main body portion m.
And, in this welding apparatus provided with a power source portion i on a base frame h side, a lower contact conductor j which electrically connects the lower electrode portion d to the power source portion intermittently, and an upper contact conductor k which electrically connects the upper electrode portion e to the power source portion i, are attached to the electrode die portion c side. Further, as shown in FIG. 11, in case that vertical face of the welded object f placed on the lower electrode portions d is welded, lateral welding electrode pressurizing cylinder guns g pressed in lateral direction to the welded object f to weld are arranged on the upper base portion b.
However, this conventional welding apparatus has following problems 1 through 5.
1 Cost of the electrode die portion c is high and the electrode die portion c becomes large for contact space above the lower base portion a because the lower contact conductor and the upper contact conductor k are arranged on the electrode die portion c side.
2 Current efficiency is bad and electro corrosion (roughness on contact point caused by spark generated by roughness of the surface and insufficient contact pressure) is generated on current contact face of upper die for long current passage (between the power source portion i and the electrode die portion c).
3 The vertical electrode pressurizing cylinder gun g (shown in FIG. 10) requires labor because the piston rod portion n must be removed from the main body portion m when diameter and length of the piston rod portion n, diameter of the tip electrode portion, etc. are changed, and damaged piston rod portion n is changed.
4 In case that welding spot on the vertical face of the welded object f is near an end portion of the lower base portion a, the gun attachment member p and the cylinder gun g are not arranged within the die (protrude from the die) for that the lateral electrode pressurizing cylinder gun g is attached in lateral direction to a gun attachment member p (as shown in FIG. 11). And, position of welding spot (number of welding point) is restricted thereby.
5 Quality of welding is greatly influenced by dispersion of electric current. For reducing the current dispersion, regulation of length and cross-section of the current passage from the power source portion i to welding position, change of welding order on simultaneous welding points, etc. are conducted based on results of measurement of the welding current and destructive examination of the welded product conventionally. This conventional method lacks stability of welding quality because influence of electrode state and deformation of the welded object f on the current of each welding point is not detected.
To solve the problems above, it is therefore an object of the present invention to provide a welding apparatus with which constructional simplification and reduction of production cost can be achieved, working efficiency is improved, and quality of welding can be stabilized.